The invention is related to the field of audio busses and in particular to low impedance stereo audio busses.
With the increase in electronic systems in the home, office and automotive environments, many of them have audio outputs. Currently, most of these devices, such as radios, CD players, mobile phones, television and similar devices have separate audio output signals activating separate speaker systems or recording devices.
Currently, there is a need for a low impedance stereo audio bus which interfaces a plurality of audio signal sources and permits access to a single stereo speaker system and/or electronic storage device which eliminates redundancy and multiple connectors.
The low impedance stereo audio (LISA) bus provides for parallel connection of a virtually unlimited number of audio sources called transmitters to one or more receivers such as a stereo speaker system. The low impedance stereo audio bus allows summing or mixing of selected transmitters, and is architected as a two-channel balanced differential, low impedance interface. The frequency response of the bus is essentially flat from 20 Hz to 20 kHz making it appropriate for all audio applications, including audiophile, and is designed to be compliant with typical automotive E.M.C. requirements.
The LISA bus has a core transmitter circuit connected to each output provided by each transmitter. For example, for a stereo transmitter, the LISA bus will have a core transmitter associated with each of the two audio outputs. Each core transmitter will generate a pair of balanced differentiated outputs for each output of the transmitter. The LISA bus also has at least one pair of core receivers at a location remote from the core transmitter. The balanced differentiated outputs of all of the core transmitters are connected in parallel to the inputs of the core receivers. The core receivers combine or reunite to a pair of balanced differentiated outputs to reproduce the stereo audio signals received from the core transmitters. A master control arbitrates which transmitter or transmitters have access to the receiver and at what relative output level.
If not provided elsewhere in the transmitters, each core transmitter will include a muting circuit, a full-scale adjustment amplifier controlled by a master control. For complex transmitters, a step attenuator circuit controlled by a master control will also be included. The core receiver may include a gain compensation circuit when two or more receivers are connected to the LISA bus. The gain of the LISA bus is unity with its output signal to the receiver being substantially equal to the input signal received from the transmitter.
One advantage of the LISA bus is that the transmitters and receivers are simply connected in parallel resulting in minimum wiring and interconnection complexity.
Another advantage of the LISA bus has a maximum reliability because the transmitters are connected in parallel and there is no need to route signals in series through other components. Hence, failure of one connected component does not render the bus inoperable.
Still another advantage is that two or more transmitters may access the LISA bus simultaneously.
Another advantage is that multiple receivers may be connected to the LISA bus by providing gain compensation in the associated core receivers and output level control may be provided in the core transmitter.
Still another advantage is that the master control controls which transmitter or transmitters will have access to the LISA bus and at what output level.
Another advantage of the LISA bus is that the master control monitors how many transmitters and receivers are connected to the LISA bus.
These and other advantages will become more apparent from reading the detailed description in conjunction with the drawings.